Yes just one knee, but I'd add another 20k onto the costs for all the follow up, physio etc. It may reoccur or it may not, depending on lifestyle. I think mine occurred from playing football on hard surfaces for many, many years, so If I give that up, less chance of it reoccurring. I also had a friend in New Zealand have the same surgery, after years of running. Shes recovered and has gone back to running daily at 62. Everyone's knees are different, but remember a knee replacement is the end game, if you can delay that as long as possible, that would be my preference.